High & low...all about the condition & model of course. Get a vac like you describe above for free, get the obligitory new belt, & or cord, & or bulbs, & or filters, & or bags, & or missing attachments...then pay yourself say minimum wage for the time spent cleaning it up, oh & lets not forget gas costs driving around finding these vacs.
(sigh) well, its no get rich quick scheme in my experience.
score a NIB (or at least looks it) vintage vac of some renown, well that keeps ya hooked. See the Vanguard in the vintage threads...shazaam!